This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. P2002-40942, filed on Feb. 19, 2002, the entire contents of which are incorporated herein by reference.
The present invention relates to an X-ray computed tomography which performs a multi-slice scan for obtaining medical images. The present invention further relates to a method of multi-slice scan in such an X-ray computed tomography apparatus.
An X-ray computed tomography apparatus (hereinafter referred to as a CT apparatus) is known to provide images of a medical examination object, such as a patient, (hereinafter referred to as a specimen) based on the intensity of an X-ray transmitted through the specimen. The images provided by the CT apparatus play an important role in a variety of medical practices including a diagnosis of a disease, a treatment, and a medical operation planning. Imaging by the CT apparatus is now being realized using a latest technique, such as, for example, a real-time image reconstruction and a multi-slice scan.
The real-time image reconstruction is a technique of reconstructing a present image by utilizing a part of projection data acquired for the previous image as a part of projection data for the present image. Here, the projection data are data obtained by scanning a predetermined part of the specimen. The scan is realized by rotating an X-ray tube radiating an X-ray and an X-ray detector around the specimen and by obtaining X-ray data transmitted through the specimen. An advantage of the real-time image reconstruction is to display an image based on the reconstructed image nearly at the same time as the scan of data for the image even if a time delay for a display processing is considered. The real-time image reconstruction technique is described in detail in Japanese Patent No. 3090400, for example.
Nowadays, an examination using a contrast agent is performed to enhance a predetermined part of the specimen, by injecting the contrast agent in the specimen. Accordingly, it becomes easier, with a contrast-enhanced image, to recognize a specific organ or a predetermined part inside the body of the specimen and, for example, to determine whether there is a tumor or not. Such a contrast-enhanced image is obtained, for example, by scans in the CT apparatus. Since, however, it takes a little time for the contrast agent to reach a predetermined (or desired) part of the specimen after the injection, it has not been so easy to obtain a preferably contrast enhanced image in the CT apparatus. Sometimes the image may be one before the contrast agent has appropriately reached the predetermined part. Or sometimes the image may be one after the contrast agent has already passed the predetermined part.
Therefore, one of the solutions for the above timing problem is adoption of the real-time image reconstruction technique to such an examination with the contrast agent. The examination may be performed as follows. First, a monitoring scan (hereinafter referred to generally as a pre-scan) is implemented at a position adjacent to the predetermined part of the body. Further, the pre-scan is helpful for monitoring an appearance of the image contrast enhancement. After the image contrast enhancement has appeared in the pre-scan, an image scan is implemented for obtaining a contrast-enhanced image of the predetermined part. Since images may be displayed in the monitor of the pre-scan substantially in real time, using the real-time image reconstruction technique, the image contrast enhancement may appear in real-time, Therefore, it may be possible to see the right time to move on to the image scan.
There seems to be no problem when such a contrast enhancement examination described above is implemented in a single-slice scan in each of the pre-scan and the image scan in a conventional CT apparatus. From another point of view, however, the single-slice scan is not so preferable. This is because it usually takes quite a long time to complete the image scan over a predetermined range of the body of the specimen and causes the specimen to be exposed unnecessarily to a large amount of radiation. As an exemplary solution for this problem, another latest technique is known as a multi-slice scan technique.
The multi-slice scan is a technique of obtaining a plurality of projection data of the specimen in a single rotation scan. Application of the multi-slice scan to the image scan described above can realize a reduction of a great deal of scanning time and of an X-ray exposure to the specimen. On the other hand, however, the pre-scan described above does not require such a multi-slice scan. As explained above, the pre-scan is only for monitoring an appearance of the image contrast enhancement. Therefore, the multi-slice scan is rather problematic to the specimen since the specimen is likely to be exposed to more radiation, compared to the radiation in the single-slice scan.
According to a first aspect of the present invention, there is provided an X-ray computed tomography apparatus, which comprises an X-ray generator configured to generate a first X-ray in a pre-scan mode and a second X-ray in an image scan mode. Additionally, an X-ray detector is used and configured to detect a first transmission X-ray exposed through a specimen to a first exposure width of the X-ray detector along a body axis of the specimen, resulting from the first X-ray at a first scanning position in the pre-scan mode and to detect a second transmission X-ray exposed through the specimen to a second exposure width of the X-ray detector along the body axis of the specimen, resulting from the second X-ray at a second scanning position in the image scan mode. The first exposure width is narrower than the second exposure width Further, the apparatus includes a controller configured to control the first scanning position and the second scanning position, and a display configured to display a first image based on the first transmission X-ray detected by the X-ray detector and a second image based on the second transmission X-ray detected by the X-ray detector.
According to a second aspect of the present invention, there is provided an X-ray computed tomography apparatus, which comprises an X-ray source configured to radiate an X-ray to a specimen, a collimator configured to vary a collimating width, along a body axis of the specimen, which determines a X-ray width exposed to the specimen, and a detector, comprising a plurality of detecting elements along the body axis, configured to detect a transmission X-ray transmitted from the specimen. The apparatus further includes a data acquisition unit, comprising a plurality of data acquisition elements along the body axis, configured to acquire output data of the detector and an implementing unit configured to implement a scan around the specimen with the X-ray source and the X-ray detector. A controller is used and configured to control a scan mode to switch from a monitoring scan to an image scan, and to control the collimator to make the collimating width wider in the image scan than in the monitoring scan. The monitoring scan is for monitoring a CT number in a predetermined region of interest of the specimen. The image scan is for scanning an examining region of the specimen. Additionally, the apparatus includes a reconstruction unit configured to reconstruct a tomography of the specimen based on projection data acquired in the monitoring scan, and also to reconstruct an image of the specimen based on projection data acquired in the image scan.
According to a third aspect of the present invention, there is provided a method of performing a scan in an X-ray computed tomography apparatus. The method begins by generating a first X-ray in a pre-scan mode and detecting with an X-ray detector a first transmission X-ray exposed through a specimen to a first exposure width of the X-ray detector along a body axis of the specimen, resulting from the first X-ray at a first scanning position in the pre-scan mode. Next, the method continues by generating a second X-ray in an image scan mode, displaying a first image based on the first transmission X-ray and detecting with the X-ray detector a second transmission X-ray exposed through the specimen to a second exposure width of the X-ray detector along the body axis of the specimen, resulting from the second X-ray at a second scanning position in the image scan mode The second exposure width is wider than the first exposure width. The method continues by displaying a second image based on the second transmission X-ray, and controlling the first scanning position and the second scanning position.
According to a fourth aspect of the present invention, there is provided a computer program product on which is stored a computer program for performing a scan in an X-ray computed tomography apparatus. The computer program has instructions, which when executed, perform steps comprising generating a first X-ray in a pre-scan mode and detecting with an X-ray detector a first transmission X-ray exposed through a specimen to a first exposure width of the X-ray detector along a body axis of the specimen, resulting from the first X-ray at a first scanning position in the pre-scan mode. The steps continue by generating a second X-ray in an image scan mode, displaying a first image based on the first transmission X-ray, and detecting with the X-ray detector a second transmission X-ray exposed through the specimen to a second exposure width of the X-ray detector along the body axis of the specimen, resulting from the second X-ray at a second scanning position in the image scan mode. The second exposure width is wider than the first exposure width. Finally, the steps continue with displaying a second image based on the second transmission X-ray, and controlling the first scanning position and the second scanning position.